1. Field of the Invention
This invention relates to a technique of calculating an order amount in a process of producing products to be utilized in subsequent processes by using parts delivered from preceding processes, such that the parts to be delivered from the preceding processes are neither excessive nor insufficient.
2. Description of the Prior Art
A proposed technique of managing the order amount is disclosed in Japanese Laid-Open Patent Publication No. 62-57060. In this technique, a stock amount detector is provided to detect the amount of stock of parts in a space in which parts delivered from preceding processes are stored. When the detected stock amount becomes less than a reference stock amount, the shortage amount is ordered. The technique is a way of subsequently resupplying used parts.
Another technique which calculates the order amount by an MRP (Material Requirement Planning) system is disclosed in Japanese Laid-Open Patent Publication No. 63-192159. In this technique, when a product production plan is given, parts order amounts are determined from the given product production plan and such data as the parts list of the product and delivery term of the parts, etc. This technique may be called a plan correspondence system.
According to the technique of the subsequently resupplying system, in demand variation periods, the parts to be delivered may be excessive or insufficient. In production increase periods, parts are liable to be insufficient, which may lead to the stoppage of the production line. In production reduction periods, the parts to be delivered may be excessive, giving rise to excessive stock. There is a further problem that no measure is prepared to restore the normal stock state from the excessive stock.
In the plan correspondence system, when calculating the order amount, there is a possibility of failure of accord between the production plan and the actual demand because the production plan is determined on the basis of the future demand forecast. Besides, once the production plan fails to be observed due to such cause as a trouble in the production or distribution facilities, over-stock or insufficient stock of parts is brought about, and there is no means prepared for making up for the over-stock or insufficient stock of parts once brought about.